1. The field of art to which the invention pertains comprises the art of fluid handling as specifically directed to change responsive line condition units therefor.
2. Preventing excess flow in a wide variety of fluid handling apparatus is well known and exemplifying pipeline units for that purpose are the disclosures of U.S. Pat. Nos. 2,635,629; 2,656,850; 2,886,061; 3,032,067 and 3,095,899.
While such excess flow fittings have undoubtedly functioned well for their intended end uses, they have generally been regarded as unsuitable for gas distribution service in which clogging dirt and/or other foreign matter is likely to be contained. Notwithstanding, flow control is a particularly hazardous problem with gas distribution piping because of the potential consequences of introducing a combustible commodity in excess at some end use downstream. Where such piping is coupled underground, the units become increasingly unserviceable rendering it difficult if not impossible to detect problems of flow. At the same time an equally if not more hazardous problem is posed by inadvertent and undetected uncoupling of the distribution piping occasioned by careless excavation or the like in the vicinity of the buried pipe. Despite recognition of the mentioned problems it has not heretofore been known how to reliably accommodate either of the foregoing, much less resolve both in a single unitary structure.